The third generation (or “3G”) of wireless communication services promises to bring unity to a fractured worldwide cellular market. 3G systems will permit seamless travel not presently available in the splintered U.S. mobile telephone service. In addition, 3G systems promise a wide array of high-speed broadband data transmission and processing, including video, on-board navigation, and Internet access.
One wireless standard designed to support 3G services is cdma2000™, defined by the ITU in its IMT-2000 vision. Phase one of the cdma2000 standard effort, known as “1×RTT” (i.e., Radio Transmission Technology), has already been completed and published by the Telecommunications Industry Association (TIA). 1×RTT refers to cdma2000 implementation within existing spectrum allocations for cdmaOne—1.25 MHz carriers. The technical term is derived from N=1 (i.e., use of the same 1.25 MHz carrier as in cdmaOne) and the “1×” means one times 1.25 MHz. 1×RTT is backward compatible with cdmaONE networks, but offers twice the voice capacity, data rates of up to 144 kbps, and overall quality improvements.
Phase 2 of the cdma 2000 standard (cdma2000-3X) offers even higher capacity than 1X, data rates of up to 2 Mbps, backward compatibility with both 1X and cdmaOne deployments, and other performance enhancements. 3X can also be implemented in existing or new spectrum allocations, but it utilizes a broader band of spectrum. The term 3X refers to N=3 (i.e. use of three 1.25 MHz carriers). There are currently two implementations of 3X identified in the standard. The Multi-Carrier mode utilizes three 1.25 MHz carriers to deliver 3G services, while the Direct Sequence mode utilizes one 3.75 MHz carrier to deliver the same services. The mode implemented would largely depend on the operator's existing spectrum allocations and usage.
Both 1X and 3X networks provide data services such as remote access of e-mail, mobile Internet browsing, and company information. Both voice and data calls must share the available network resources such as Walsh codes. The capacity of a CDMA network to admit a given voice or data caller is determined very differently than in a TDMA network. In a TDMA network, either a time slot is available for a caller, whether data or voice, or it is not. Thus, a call admission policy in a TDMA system need merely determine how many time slots a caller needs and whether these time slots are available. In contrast to this “binary” capacity, a CDMA network has a much “softer” network capacity—the callers do not occupy discrete time slots but rather share the entire available spectrum with each other simultaneously. Thus, theoretically, so long as a Walsh code is available for use, there are no hard limits on how many calls may occupy the available bandwidth. However, because the Walsh codes have finite levels of cross correlation, as more and more users occupy the bandwidth, unacceptable bit error rates eventually result. Other factors also limit the number of users in a CDMA system. Prior art CDMA systems typically divided the total available network resources at a fixed ratio between data and voice callers. This results in certain unavoidable inefficiencies. For example, a data call is typically very bursty, resulting in unpredictable sudden demands on network resources. Apportioning these network resources at a fixed ratio means that, from time to time, the network resources allocated to data callers are unused. These unused network resources could be allocated to voice callers, but must remain unused in such prior art systems, resulting in waste of network resources.
Thus, there is a need in the art for improved call admission policies that dynamically apportion network resources between data and voice users.